In one of the most comprehensive studies of its kind, scientists from the University of Cambridge have found that the brain progresses in five “major epochs” or eras over the course of a human life.
The study published in Nature Communications analysed the brains of 3,802 people aged between zero and 90, using datasets of MRI diffusion scans, which map neural connections by tracking how water molecules move through brain tissue. The researchers thus found four pivotal “turning points” over the human life cycle, at around ages nine, 32, 66 and 83 years.
The study tracked how brains reconfigure and enable new ways of thinking as a person ages.
“We know the brain’s wiring is crucial to our development, but we lack a big picture of how it changes across our lives and why,” Alexa Mousley, the lead researcher and a Gates Cambridge Scholar, told Cambridge University. “This study is the first to identify major phases of brain wiring across a human lifespan.”
What are the five different eras?
CHILDHOOD
Era One (Dr Alexa Mousley, University of Cambridge)
During the first period of a person’s life, the brain rapidly increases in size. However, the overabundance of connections of synapses, the connections between brain cells is also being whittled down in what the researchers call “network consolidation”. Only the more active synapses survive.
The researchers also noted the brain’s susceptibility to mental health disorders, even as the brain experiences a step-change in cognitive capacity. The increasing presence of grey matter, which processes information and controls voluntary movements, and white matter, the brain’s communication system, peaks to stabilise the cortical thickness (the distance between the two), and the cortical folding, the characteristic ridges on the outer brain.
ADOLESCENCE
Era Two (Dr Alexa Mousley, University of Cambridge)
In the second era, the white matter in the brain continues to grow, refining the brain’s communication networks during this period. This is a period of neural efficiency, marked by efficient connections within specific regions in the brain and the speed of communication across the brain. The result is enhanced cognitive performance.
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Interestingly, the study shows that the process of adolescence continues until and peaks in the early thirties, the “strongest topological turning point” of the entire life span. For the longest time, it was believed that this era was restricted to the teenage years, before developments in neuroscience indicated that this process continues into a person’s 20s.
“Around the age of 32, we see the most directional changes in wiring and the largest overall shift in trajectory, compared to all the other turning points,” said Mousley. “While puberty offers a clear start, the end of adolescence is much harder to pin down scientifically. Based purely on neural architecture, we found that adolescent-like changes in brain structure end around the early thirties.”
ADULTHOOD
Era Three (Dr Alexa Mousley, University of Cambridge)
According to the study, this era, beginning at age 32, is the longest, spanning 30 years. The brain architecture becomes stable during this period, which the researchers have described as a “plateau in intelligence and personality” based on other studies. They have also found that the different regions of the brain become more compartmentalised, resulting in “segregation”.
EARLY AGEING BRAIN
Era Four (Dr Alexa Mousley, University of Cambridge)
The study notes 66 years as the next turning point, although it is relatively milder and not indicative of major structural shifts. However, the researchers noted meaningful changes in the pattern of brain networks around this age. During this period, the different regions of the brain no longer coordinate as a singular unit, but continue to work tightly together.
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This period also coincides with an incidence of dementia and high blood pressure, which impacts brain health.
LATE AGEING BRAIN
Era Five (Dr Alexa Mousley, University of Cambridge)
The final epoch of the brain becomes known at around 83 years. The study had less data for this period, given the challenge of finding healthy brains to scan. While the brain changes are similar to early ageing, there is a greater decline in whole-brain connectivity and increased reliance on certain regions.
Why are these results significant?
The results provide a new template of how the human brain works, and the different areas of vulnerability or development it may experience during each period.
“Many neurodevelopmental, mental health and neurological conditions are linked to the way the brain is wired. Indeed, differences in brain wiring predict difficulties with attention, language, memory, and a whole host of different behaviours,” said Duncan Astle, one of the co-authors of the study. “Understanding that the brain’s structural journey is not a question of steady progression, but rather one of a few major turning points, will help us identify when and how its wiring is vulnerable to disruption.”
